// ES6
import { Queryable } from 'linq-fns';

// ES5
const Queryable = require('linq-fns').Queryable;

let query = Queryable
            .from(nations)
            .join(continents, (x, y) => x.areaId === y.id)
            .groupBy(o => o.y.areaName)
            .select(x => {
                return {
                    area: x.key,
                    total: Queryable.fromSync(x.items).count() // Here will return number, not Promise<number>
                }
            })
const asyncData = query.toList() // Will return Promise<{area:string, total:number}>
asyncData.then(data => {
    console.log(data);
    // [
    //     {area: 'Euro': total: 2},
    //     {area:'South Ameria', total: 1}
    // ]
});

const FireBaseQueryale = require('linq-fns').FireBaseQueryale;
const admin = require('firebase-admin');
const serviceAccount = require('./serviceAccountKey');

admin.initializeApp({
    credential: admin.credential.cert(serviceAccount),
    databaseURL: 'https://xxx.firebaseio.com'
});

const db = admin.database();
const postsQuery = new FireBaseQueryale(db,'<yourdb>.posts');

// READ AND QUERY DATA
// ES5 Promise
postsQuery.getQuery().where('...').select('...').toList().then(x=>'...');

// Async/await
const data = await postsQuery.getQuery().where('...').select('...').toList();

// WRITE DATA
// Just call not execute to server
postsQuery.add(item);
postsQuery.remove(item);
postsQuery.update(item);

// Call this to execute 3 above methods
postsQuery.commitChanges();